The effect of pH on the Rate at which Saliva Hydrolyzes Starch
Julia, Rob
Introduction
Hydrolysis is a chemical reaction in which a chemical compound is broken down by a reaction with water. In the lab we hydrolyzed the chemical compound starch with water and added enzymes to the starch. The enzyme in saliva (ptyalin) breaks down the bond between the glucose molecules that when linked together form starch. Here is the reaction that occurs:
starch+ptyalin ---> maltose (two glucose joined together)
But in different environments enzyme activity level can vary. For example, when exposed to extreme pH levels, either acidic or basic, emzymes can denature therefore it is not able to act on the substrate, in this case, starch. The reason that extreme pH levels denature enzymes is because of the mutual repulsion between like charges. This often causes the secondary and tertiary structures to change, therefore changing the active site. The changes may or may not be irreversible.
Enzymes can also act differently from one another. Not every enzyme's peak activity happens under the same conditions. For exmaple, stomach enzymes act most efficiently in very acidic environments. There are also enzmyes from hot springs that can tolerate extremely high temperatures that most enzymes cannot withstand without denaturing.
The purpose of the lab was to see the effects that different pHs have on the rate at which saliva can hydrolyze starch.
Procedure
First we cut up a regular household potato into square inch pieces. Then we boiled 99.74 grams of cut up potatoes in a 400 mL beaker on a hot plate and waited for it to boil. While the potatos were heating up we prepared three test tubes. In the first test tube we put 1 mL of pH 4 buffer. In the second test tube we put 1 mL of pH7 buffer. In the third test tube we put 1 mL of pH 10 buffer. After the solution started to boil (which took about 15 minutes) we put 1 mL of the starch solution into the three different test tubes. We then poured each buffer into one of the three test tubes containing the starch solution. Then, we added a drop of iodine solution into each of the three test tubes containing the starch solution. When the iodine solution hit the starch it created a very dark indigo color. Last we added the enzyme, saliva. We added 1 mL of saliva to each test tube. Then we observed the three test tubes watching to see if the color was changing and if so how fast and in which test tube the color was changing first.
Results
We observed that the saliva enzyme did not work as well under the two pH extremes (pH 4 & 10). More starch was hydrolyzed in the pH 7 buffer than in the others. The results were a little surprising because the acidic and the basic solutions acted similarly. We expected to see three different results.
Observation Table:
color after...(mins)
tube #1 (pH 4)
tube #2 (pH 7)
tube #3 (pH 10)
initial
dark indigo
dark indigo
dark indigo
2
slightly lighter, still dark
a lot lighter, closer to green
in between the two extremes, still pretty dark
4
same
lighter but still a hint of blue-green
a little lighter turning purple-blue
6
same
almost clear, barely any color
same purple-blue color
8
same
clear
only a little bit lighter but basically the same
(more similar coloring to pH4 than pH7)
Conclusions
Our results showed that the more extreme the pH the harder it is for enzymes to work effectively. We found that the extremely acidic pH 4 was the most debilitating to the enzyme. The enzyme functioned best at pH 7. In the pH 10 solution the enzyme was obviously less effective than at pH 7, but more effective than in the pH 4 solution. From what we learned about enzymes we guessed that the extreme pHs denatured the enzymes by changing the secondary and tertiary structures. This causes the active site to change therefore the enzmye cannot attach to the substrate. Since the enzyme cannot attach to the substrate it cannot act as the catalyst. Overall we found that different pHs cause the enzmye saliva to hydrolyze starch at very different rates. In the extreme cases the pHs cause the saliva enzyme to stop functioning all together.
There were many sources of error. One of our main problems was that the pH buffers we had access to were already tinted a certain color. Because color was the test for our experiment this caused problems when it came to observing our experiment. In some cases we weren't sure whether the color we were seeing was indicating the presence of starch or whether it was just the color of the pH buffer. This is something we would definitely recommend changing if you have the resources. Another source of error occurred during the collecting of the saliva. A lot of foam formed on the top of the saliva and we believe that one of the test tubes received less actual saliva than 1 mL because some of the foam was included in that measurement when it shouldn't have been.
References
Selinger, Ben. Chemistry in the Marketplace. fifth. Orlando, Florida: Harcourt Brace & Company, 1998.
Table of Contents
The effect of pH on the Rate at which Saliva Hydrolyzes Starch
Julia, Rob
Introduction
Hydrolysis is a chemical reaction in which a chemical compound is broken down by a reaction with water. In the lab we hydrolyzed the chemical compound starch with water and added enzymes to the starch. The enzyme in saliva (ptyalin) breaks down the bond between the glucose molecules that when linked together form starch. Here is the reaction that occurs:starch+ptyalin ---> maltose (two glucose joined together)
But in different environments enzyme activity level can vary. For example, when exposed to extreme pH levels, either acidic or basic, emzymes can denature therefore it is not able to act on the substrate, in this case, starch. The reason that extreme pH levels denature enzymes is because of the mutual repulsion between like charges. This often causes the secondary and tertiary structures to change, therefore changing the active site. The changes may or may not be irreversible.
Enzymes can also act differently from one another. Not every enzyme's peak activity happens under the same conditions. For exmaple, stomach enzymes act most efficiently in very acidic environments. There are also enzmyes from hot springs that can tolerate extremely high temperatures that most enzymes cannot withstand without denaturing.
The purpose of the lab was to see the effects that different pHs have on the rate at which saliva can hydrolyze starch.
Procedure
First we cut up a regular household potato into square inch pieces. Then we boiled 99.74 grams of cut up potatoes in a 400 mL beaker on a hot plate and waited for it to boil. While the potatos were heating up we prepared three test tubes. In the first test tube we put 1 mL of pH 4 buffer. In the second test tube we put 1 mL of pH7 buffer. In the third test tube we put 1 mL of pH 10 buffer. After the solution started to boil (which took about 15 minutes) we put 1 mL of the starch solution into the three different test tubes. We then poured each buffer into one of the three test tubes containing the starch solution. Then, we added a drop of iodine solution into each of the three test tubes containing the starch solution. When the iodine solution hit the starch it created a very dark indigo color. Last we added the enzyme, saliva. We added 1 mL of saliva to each test tube. Then we observed the three test tubes watching to see if the color was changing and if so how fast and in which test tube the color was changing first.Results
We observed that the saliva enzyme did not work as well under the two pH extremes (pH 4 & 10). More starch was hydrolyzed in the pH 7 buffer than in the others. The results were a little surprising because the acidic and the basic solutions acted similarly. We expected to see three different results.
Observation Table:
(more similar coloring to pH4 than pH7)
Conclusions
Our results showed that the more extreme the pH the harder it is for enzymes to work effectively. We found that the extremely acidic pH 4 was the most debilitating to the enzyme. The enzyme functioned best at pH 7. In the pH 10 solution the enzyme was obviously less effective than at pH 7, but more effective than in the pH 4 solution. From what we learned about enzymes we guessed that the extreme pHs denatured the enzymes by changing the secondary and tertiary structures. This causes the active site to change therefore the enzmye cannot attach to the substrate. Since the enzyme cannot attach to the substrate it cannot act as the catalyst. Overall we found that different pHs cause the enzmye saliva to hydrolyze starch at very different rates. In the extreme cases the pHs cause the saliva enzyme to stop functioning all together.There were many sources of error. One of our main problems was that the pH buffers we had access to were already tinted a certain color. Because color was the test for our experiment this caused problems when it came to observing our experiment. In some cases we weren't sure whether the color we were seeing was indicating the presence of starch or whether it was just the color of the pH buffer. This is something we would definitely recommend changing if you have the resources. Another source of error occurred during the collecting of the saliva. A lot of foam formed on the top of the saliva and we believe that one of the test tubes received less actual saliva than 1 mL because some of the foam was included in that measurement when it shouldn't have been.
References
Selinger, Ben. Chemistry in the Marketplace. fifth. Orlando, Florida: Harcourt Brace & Company, 1998.
Ganong, Barry. Enzyme Hydrolysis of Starch.
Logan, R. Enzyme Activity.